🚀 go-pugleaf

edhall@rand.org (Ed Hall) writes:

>One composite technique is to use linear prediction to derive a
>spectral envelope and a phase vocoder to shift the excitation spectrum.

>A phase vocoder models a sound as a summation of sine waves, using
>either an FFT or filterbank to determine the frequencies; these can then
>be shifted proportionally such that the ratios between the frequencies
>are maintained while the overall pitch is changed.  When a phase vocoder
>is used by itself, the magnitudes of the original frequencies are
>usually imposed on the corresponding shifted frequencies.  This means
>that the formants shift as well.  However, by imposing the original
>spectral envelope on the shifted frequencies the formants can be
>maintained even though the pitch has changed.

>The CSOUND package contains both linear prediction and phase vocoder
>modules, among other goodies.  It is available for FTP at
>media-lab.media.mit.edu.  

I had better luck:  ftp ems.media.mit.edu:/pub/Csound/csound.tar.Z

>CSOUND is big, complex, and hard to use.  If
>you're serious about computer sound synthesis, though, it is well worth
>the effort.  It runs under various Unices, the NeXT, and the Mac. (I've
>compiled and run it on a SPARC and a '486, more or less out-of-the-box.)

>		-Ed Hall
>		edhall@rand.org

alvin  

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